Our objective is to deduce the mechanism of mutagenesis of formaldehyde in a higher organism by characterizing the ultimate defects that it produces. Our strategy is to make mutations in the alcohol dehydrogenase gene of Drosophila melanogaster by feeding flies food that had been treated with formaldehyde. Those organisms that lack active alcohol dehydrogenase - alcohol dehydrogenase negatives - will be isolated and their alcohol dehydrogenase gene cloned. A fraction of the mutants are expected to bear small intragenic deletions and these will be characterized by restriction mapping and DNA sequencing. Most of the mutants obtained in previous experiments have proven to be large deletions. We will characterize these mutants by using the technique of chromosome walking. We will build a library of a series of large overlapping cloned DNA fragments that begin at the alcohol dehydrogenase gene and branch out in either direction. These will be used as probes to locate the suture region of the deletion. The DNA fragment containing the suture region will be cloned from the mutant flies and the suture region sequenced. This study will be carried out on repair-proficient strains of Drosophila and will be repeated in several repair-deficient strains as well. Because it is a very widely used compound, nearly the entire population is exposed to formaldehyde on a regular basis. Yet much evidence exists that it is a potent genotoxic agent. By understanding its mechanism of action, we may be able to more intimately evalute its genetic and carcinogenic risk to humans.